The pavement design industry is moving towards the use of mechanistic principles in designing flexible
pavements. To determine the resultant strains in the pavement system using these principles, two material
properties are required; 1) modulus and 2) Poisson’s ratio. In flexible pavement design, the required modulus
can be determined either in the laboratory or in the field. In the lab, the dynamic modulus and resilient modulus
tests are used to determine the modulus values of asphalt and unbound materials, respectively. In the field, the
Falling Weight Deflectometer (FWD) is commonly used to determine the modulus of the various materials.
However, the value of the Poisson’s Ratio is usually assumed. This research project encompassed the
evaluation of whether or not the Poisson’s Ratio can be measured using the same test procedures commonly
used to obtain the modulus values for flexible pavement design (i.e. – dynamic modulus test for asphalt and
resilient modulus test for unbound materials). The research project also evaluated the sensitivity of pavement
performance and the FWD backcalculation procedure when varying the magnitude of the Poisson’s Ratio
parameter.

The results showed that the Poisson’s Ratio can readily be measured during the dynamic modulus (AASHTO
TP62) test procedure using a radial LVDT measuring system. Tests conducted on a number of asphalt mixtures
also showed that there is a relationship between modulus and Poisson’s Ratio (as modulus decreases, Poisson’s
Ratio increases). However, some discrepancies were found between the measured and predicted values when
using the Poisson’s Ratio prediction equation provided in the Mechanistic Empirical Pavement Design Guide
(MEPDG) software, especially when higher PG asphalt binder grades were used. The results also showed that
the Poisson’s Ratio should not be measured during the resilient modulus (MR) test for unbound materials. This is
mainly due to the fact that the MR test does not typically test the material in its natural linear elastic state, which is
where the Poisson’s Ratio concept is valid. Sensitivity analysis work with the FWD backcalculation and using the
MPEDG illustrated how the predicted pavement response is affected by the selected Poisson’s Ratio value.